How much will sea level rise?

… is the question people have been putting a lot of thought into since the IPCC AR4 report came out. We analysed what was in the report quite carefully at the time and pointed out that the allowance for dynamic ice sheet processes was very uncertain, and actually precluded setting a upper limit on what might be expected. The numbers that appeared in some headlines (up to 59 cm by 2100) did not take that uncertainty into account.

In a more recent paper, our own Stefan Rahmstorf used a simple regression model to suggest that sea level rise (SLR) could reach 0.5 to 1.4 meters above 1990 levels by 2100, but this did not consider individual processes like dynamic ice sheet changes, being only based on how global sea level has been linked to global warming over the past 120 years. As Stefan discussed, any non-linear or threshold behavior of ice sheets could lead to sea level rising faster than this estimate. Thus, otherwise quite conservative voices have been stressing the ‘unknown unknown’ nature of this problem and suggesting that, based on paleo-data (for instance), it was really hard to rule out sea level rises measured in feet, and not in inches. (Note too, the SLR is very much a lagging indicator, and will continue for centuries past the time that atmospheric temperatures have stabilised).

The first paper to really try and assess the future limits on dynamic ice sheet loss appeared in Science this week. Pfeffer et al looked at the exit glaciers for Greenland and West Antarctica and made some back of the envelope calculations of how quickly the ice sheets could dynamically drain.

Good news: they rule out more than 2 meters of sea level coming from Greenland alone in the next century. This is however more than anyone has ever suggested and would be comparable to the amount that disappeared at the Eemian (125,000 years ago) (see this post for more on that).

Bad news: they can’t rule out up to 2 meters in total.

In summary, they estimate that including dynamic ice sheet processes gives projected SLR at 2100 somewhere in the 80 cm to 2 meter range, and suggest that 80 cm should be the ‘default’ value. This is remarkable in a number of ways – first, these are the highest estimates of sea level rise by 2100 that has been published in the literature to date, and secondly, while they don’t take into account the full uncertainty in other aspects of sea level rise considered by IPCC, their numbers are significantly higher in any case. And this week the Dutch ‘Delta Commission‘ published its estimate of sea level rise that the Dutch need to plan for (p111): 55 to 110 cm globally and a bit more for Holland, based on a large number of scientists’ input. [Clarifying update: this is meant to be a “high end estimate”.]

Lest readers think this is no big deal, the estimates for the number of people who would be affected by 1 meter of sea level rise is more than 100 million – mainly in Asia. Of some recent relevance is the fact that the storm surge caused by Gustav in New Orleans was within 1 foot of the top of the levees. Another 3 ft caused by global sea level rise would have put a lot more water into the ‘bowl’.

Thus better estimates of sea level rise from ice sheets remain a high priority for the climate community. More sophisticated models and deeper understanding are coming along and hopefully those results will be out soon.

We were going to leave it at that, but we’ve just seen the initial media coverage where this result is being spun as a downgrading of predictions! (exemplified by this Reuters piece, drawing mainly from the U. Colorado press release). This is completely backwards. We stress that no-one (and we mean no-one) has published an informed estimate of more than 2 meters of sea level rise by 2100. Tellingly, the statement in the paper that suggests otherwise has no reference.

There have certainly been incorrect assertions and headlines implying that 20 ft of sea level by 2100 was expected, but they are mostly based on a confusion of a transient rise with the eventual sea level rise which might take hundreds to thousands of years. And before someone gets up to say Al Gore, we’ll point out preemptively that he made no prediction for 2100 or any other timescale. The nearest thing I can find is Jim Hansen who states that “it [is] almost inconceivable that BAU climate change would not yield a sea level change of the order of meters on the century timescale”. But that is neither a specific prediction for 2100, nor necessarily one that is out of line with the Pfeffer et al’s bounds.

Thus, this media reporting stands as a classic example of how scientists get caught up trying to counter supposed myths but end up perpetuating others, and miss an opportunity to actually educate the public. The problem is not that people think that we will get 6 meters of sea level rise this century, it’s that they don’t think there’ll be anything to speak of. Headlines like that in the Reuters piece (or National Geographic) are therefore doing a fundamental disservice to the public understanding of the problem.

Update: Marc Roberts sends along this cartoon illustrating the problem… (click for full size).

Guy #150- None of the IPCC reports are “like with like” with each other in terms of methods, which evolve and change over time, so that concern is irrelevant. What is “like for like” is the fact that each IPCC provides “best estimates” for the future. I find that selecting among “best estimates” and presenting only half the story to be misleading, especially when the other half of the story suggests some very different conclusions.

Is it possible that the higher surface temperatures north of Siberia and Alaska are due to methane being released from hydrates in the sea shelf, creating a more intense local greenhouse effect?

[Response: very unlikely. Remember that most of the impact from greenhouse gases globally occurs because of feedbacks – and those are often non-local. For instance, water vapour changes in these regions are less affected by local changes in temperature than they are by conditions over the upstream oceans. -gavin]

“Shakhova and her colleagues gathered evidence for the loss of rigor in the frozen sea floor in a measuring campaign during the Siberian summer. The seawater proved to be ‘highly oversaturated with solute methane,’ reports Shakhova. In the air over the sea, greenhouse-gas content was measured in some places at five times normal values. ‘In helicopter flights over the delta of the Lena River, higher methane concentrations have been measured at altitudes as high as 1,800 meters,’ she says.”

Edward Greisch
“You shouldn’t have built a city that close to the water in the first place. In the present place, you should be moving the city, except for the harbor itself, to a new location at least 100 meters above sea level.”
Well said. This cannot be over emphasized. Rising seas is not the only peril along a coast. We all love to look at the blue water, I get that but there are unstoppable forces in nature like the long shore current, to name one, even if sea level weren’t rising, which it is.

#152 – but hold on, you concede that 2007 is quantitively different, and yet you also concede the reasons why 1990 is quantatively different. Sure the science is always advancing, but 1990 left out aerosols completely, and 2007 left out dynamic ice-sheet processes – both of which are quite different and should not be compared like-for-like with 1996 or 2001, which attempt to be all-encompasing (please someone put me right if I have this wrong!!!)

But I seem to have made this point several times, and Stefan has answered too (btw, I don’t think you’ve responded to his inline of #136, which is new). You’ll forgive me, but I have to conclude that you have some sort of agenda here by not simply supporting the good (and uncontentious) work of other scientists and accusing them of some form of deception. Perhaps in the interests of greater understanding it would help us all if you would elaborate as to what this agenda is?!

Overselling or misrepresenting science is not good no matter who does it. My original response to this thread makes this same point in the context of the claim that “no-one (and we mean no-one) has published an informed estimate of more than 2 meters of sea level rise by 2100”. This is just wrong.

Here is what Jim Hansen said:

“As an example, let us say that ice sheet melting adds 1 centimetre to sea level for the decade 2005 to 2015, and that this doubles each decade until the West Antarctic ice sheet is largely depleted. This would yield a rise in sea level of more than 5 metres by 2095.

When science is oversold you will indeed get news stories that say that a prediction of 2 meters is a reduction. Sorry, but it just can’t have be both ways.

Similarly, Stefan (#136, thanks for the pointer) says that his take-away line from his article on evaluating IPCC projections was imprecise, saving the effort of adding “TAR” to that last sentence, sorry, nothing personal or malicious, but I find that very misleading.

You are of course free to disagree ;-) And if you are interested in my “agenda” on climate policy or science policy, feel free to visit our site, where you’ll find more on that than you would want.

[Response: Roger, are you criticising Jim Hansen or are you criticising us? Your quote of Jim’s speculation seems to imply that him saying this is the definition of the ‘science being oversold’ – I do not accept that characterization of his thought experiment but neither do I think that this counts as an ‘informed estimate’ – no ice sheet data or modeling was used, and his statement later on in the same paper as well as this one makes it clear that this is only very loosely constrained speculation. If the mere fact of Jim publishing his thoughts on the matter is ‘overselling the science’, presumably you think he should have been prevented from doing so? But if prior restraint on Jim is not what you propose (and that has a bad track record of effectiveness), then it must be that someone else is guilty of this overselling – who might that be? and what do you think they should have done instead? – gavin]

The terms of the law authorizing construction actually require a 99.9999% probability of surviving a 200-year return event. The project is near sea level, so floods and levee breaches are included as events the facilities must survive. In this vein, I would strongly endorse requiring all of the California legislators and members of the US Congress to take an extended course in statistics. Because of the language in the law, the PE is under some stress with respect to bonding and liability.

How many standard deviations is the current Arctic Sea Ice condition from say the 1979-2000 baseline? (Six, you say? We have a one- in a million event.) We are already in a long tail event. I can hear E. Deming saying, ”The system is in not in control. You have not looked at all of your data, and you have not thought through the implications of the data and observations that you have looked at. You have not done the math. You have not told the truth.”

Read Deming and tell me the system (Earth) is in control. Tell me you have absolute confidence in the quality of the data going into the GCM. Tell me that the precision and confidence of that data is known, and carried through all calculations. Tell me that nothing has been left out of the GCM (such as dynamics of ice sheets.) Tell me that feedbacks such as CO2 release from permafrost and clathrates have been fully accounted. Tell me that ocean currents are well calculated and reorganizations of ocean currents will be calculated as they occur. Tell me we understand in detail how an open Arctic Ocean will affect rain on the GIS. Tell me that we understand how a warming southern ocean will affect the base of the WAIS. Tell me that climate guys with the most accurate predictions in get the most pay, and there is no premium for downplaying the dangers of global warming.

By the standards of data quality established by the US EPA for CERCLA, the data quality in climate science is poor. (I helped write some of the early drafts of ASQC-E4 and the ASTM data standards for human health risk assement.) And, yet the risks to humans from global warming is at least as great as the risks form releases of toxic materials Our risk assement data for impacts from global warming should be as good as our risk assement data for toxic releases.

Current GCM do not include behavior of ice sheets, and thereby cannot be used to estimate the impacts of global warming. Sea level rise impacts melting of permafrost (release of CO2), availability of resources (i.e., stock exchanges), availability of fuel, organic chemicals, fibers, and fertilizer, transportation. The issues that bother me most is the failure to consider loss of food production resources (fertilizer/fuel) as sea level rises. Lack of food due to lack of fertilizer/fuel would shut this place down real fast Any analysis that does not fully consider these issues is incomplete.

Until we have good quality data and all factors are included in the calculation of the impacts of global warming, then guesses about sea level rise from ice dynamics are not better planning tools than the IPCC estimate of sea level rise from thermal expansion. Such guesses are not a basis for prudent planning. Moreover, any such guesses that do not include all known factors inspire false confidence. Hence, my desire for a maximum plausible SLR value that includes all factors and data

Roger, I find it fascinating to see you lecturing scientists about how science works. Your misrepresentation of Stefan’s words is simply a case of pulling something out of context, then trying to whip it up into a controversy about the credibility of scientists. Your words are perjorative, and unfairly so. There is simply no justification for your use of the word “spin” in the way you have.

Ps — Aaron, I’m sure whatever law you’re talking about is by its terms referring to prior 200-year event experience. They weren’t requiring accuracy in 200-year forecasting of weather at that location.

Mr. Aaron Lewis has spoken of rainfall in Greenland weakening the ice sheets. I have seen measurements and estimates of annual precipitation in Greenland, but I do not recall any that separated out rain as opposed to snow. I would appreciate pointers. I would also expect rain to cause a drop in the surface height, and rain on the flanks should steepen the surface slope.
Now that we have many lasers and such, has anyone undertaken careful altimetric studies before and after a rainstorm in Greenland ?

Aaron Lewis (156) wrote “The terms of the law authorizing construction actually require a 99.9999% probability of surviving a 200-year return event.” COuld you kindly explain more fully. The law where? Are these (essentiaaly) the same terms throughout the developed world?

I read THE RISING-JOURNEYS IN THE WAKE OF GLOBAL WARMING, a novel (see http://www.risingglobalwarming.com/ ). One of the points they make is a few feet of sea rise is enough to cripple California’s water system — and CA can’t really afford that with diminishing potable and ag water from GW & other causes.

Their scenario is interesting. In addition to AGW increasing the sea level, some really dangerous types of volcanoes under the Antarctic erupt and melt a lot of ice pronto, which raises the sea a lot in a much shorter time. It’s farfetched, but how close the CA water system is to sea level is real, and pretty scary….I suppose someone it working on some dikes over there.

A fair percentage of the comments here are stating we can expect sea levels to rise by a minimum of 2 metres by 2100. This seems to be based on the idea of a vastly increased global ice melt. Nearly all of the examples of melt seem to involve the NH only, why?

90% of the global ice is contained in the SH so why is there hardly mention of it? A 5% increase in SH ice is equal to 50% of total NH ice after all.

I would hope that this lack of discussion in SH ice, which after all is the overwhelming factoe in any sea level rise based on ice melt, is not due to the fact there is no evidence of decreasing ice levels in the SH. Indeed Antarctica, which contains most of the worlds ice, has been geting colder for some time now with evidence of increasing ice levels.

For these, what could almost be called alarmist, sea rise levels mentioned here to come to pass, the average sea level rise needs to be 20mm per year for the whole of the 21st century. Where is the evidence that this is a probability? Sea level rises shows no sign of the huge acceleration that would be required to get anywhere near this. Indeed it is quite the opposite at the moment, unusually we seem to have had no rise at all in sea levels for the last 3 years or so!

The other current indicators do not seem to support any such speculations. Sea temperatures have shown a slight cooling over the last few years. Global temperatures have stalled since 2001 with a slight cooling in fact.

Basing everything on computer models which are slowly moving away from actual Earth conditions does not seem to be ‘proper’ science to me.

I actually don’t seem to see much effort being put into trying to explain and calculate the reasons and factors which seem to have stopped the, hypothesised, inexorable rise in global temperatures caused by Mankinds CO2 emissions. Emissions which have continued to increase post the models.

I would hope that this is not because any proven results would completely undermine the whole AGW theory, which is based on the theory that CO2 was the ‘last man standing’ when all other natural factors were eliminated because of their calculated maximum effect.

I suppose the idea out there is that, if a combination of natural factors could produce that amount of cooling then, it is just as likely that a similar combination of factors could cause a similar amount of warming. Something that the hypothesis of AGW can not allow.

The pumps which lift the water from the Sacramento/San Joaquin rivers are just about at current sea level in the Delta. And there are dikes around the islands in the Delta, since some of the farmland is now 25 feet (7.6 meters) below current sea level due to the erosion of peat soil.

The transport of fresh water to Southern California is part of the reason our governator is reviving the plan to build the “Peripheral Canal” to route water around the Delta. But as I keep pointing out to the engineers, the old Peripheral Canal was designed without sea level rise in mind. One of Schwarzenegger’s task forces is urging him to prepare for a sea level rise of 55 inches (1.4 meters) by the end of this century.

In its report to the governor, the task force surveyed 23 state and federal agencies to learn their sea-level predictions. Only two, both closely associated with the task force itself, have considered a potential rise of 55 inches. Those are the CalFed Bay-Delta Program and the Delta Risk Management Strategy, a research effort by the Department of Water Resources.

Other estimates for 2100 fall between 28 and 35 inches. But 11 agencies have no estimate to guide their work, Delta Vision found, including Caltrans, the U.S. Army Corps of Engineers and Bureau of Reclamation, the state Public Utilities Commission and Water Resources Control Board.

I am not criticizing Hansen, he is free to issue whatever prediction he wants. Back on point, the Colorado press release said nothing about “informed estimates”, that was your invention. It simply said:

“Despite projections by some scientists of global seas rising by 20 feet or more by the end of this century as a result of warming, a new University of Colorado at Boulder study concludes that global sea rise of much more than 6 feet is a near physical impossibility.”

I think that it has been pretty clearly established that “some scientists” have made such “projections,” whether they are “loosely constrained speculation” or whatever you wish to call them is irrelevant.

You claim that “The problem is not that people think that we will get 6 meters of sea level rise this century . . .”, well it is a problem if you want people to view 0.8 or 2 meters as a large number, because once there have been uncontested worldwide headlines about 5 meters (or even 25 meters!) this century, 2 meters just isn’t newsy, and indeed looks like a big step back.

In this context, complaining about completely accurate press releases approved by your colleagues as “spin” or labeling entirely appropriate media interpretations as misleading just isn’t productive. That happens to be my opinion, I respect that you see things differently.

We’ve aired our different points of view for all to see, and you can have the last words on this exchange if you’d like ;-)

[Response: I think you are failing to see the wood for the trees here. On any issue I can find someone, somewhere who has said something that my latest results are smaller or greater than. If my model says rainfall will increase 3%/deg C, then I can claim it’s much less than some scientists have said, or much more than others. Either way my statement will be accurate, but the framing will impart spin to the result and lead to completely opposite headlines “Rainfall to raise faster than expected” or “Rainfall raise not as bad as expected” – since both things cannot be true, one must perforce be misleading. Which depends on the context of what is ‘expected’. The implication is that it is a general expectation, not just what one person thinks. General expectations in the climate community have been usefully written down, reviewed, critiqued and summarised in assessment reports like the IPCC, the NRC or the CCSP reports.

We chose the words in the above post quite carefully, because there is a big difference between someone saying something speculatively and something being generally expected. Whatever the merits of Jim’s statements, you cannot claim that they are the consensus – that was after all the point he was making in the ERL paper. As to “uncontested worldwide headlines” claiming 5 or 25 m sea level rises by 2100, you are flat wrong. Headlines, yes. Uncontested? No – and I provided examples of that contestation above (but even I am hard pressed to find a headline claiming 25m – citation?).

By framing their result as a contrast to Hansen’s perceived views instead of the IPCC report, Pfeffer et al opted for a public airing of a argument that only a small number of scientists would ‘get’, instead of making a statement that would educate the much larger number of people who had heard about or read the IPCC report which clearly stands as the most recent community statement on this topic. That is a lost opportunity. Whether critiquing media reports is productive depends very much on whether the community learns to do better – personally I think they can – in particular by taking note of the wider context in which their news will appear. – gavin]

The problem with the large sized rise in sea level is there is no time frame attached. Gore does it, Greenpease does it (and is being sued in Spain). Here is an example:

“James Hanson, a NASA Scientist, has demonstrated that warming above 1.5 -1.7 degrees is likely to cause the melting of both the West Antarctic and Greenland Ice Sheets. If these enormous blocks of ice melt, global sea level would rise by 25metres, flooding major cities and river deltas – the world would be a very different place. To prevent this warming will require reductions of at least 100% by 2030.”

People get the distinct impression this is soon, 100 years at most. What people do not understand is it would take at least a 1000 years for Hansen’s prediction to come true and produce that much increase. Thus without giving a time frame with the predictions is grossly misleading. At least now with this paper we have an upper limit proposed by 2100. So now the big radical predictions will have to be in perspective.

Besides, in 1000 years it won’t matter. There will be far fewer people on the planet, cities will be largely abandoned, because we will have consumed the last of the available fossile fuels 900 years before.

Here is another series of misrepresentations from the Bali conference last year:

Jakarta airport to be under water by 2035. (the airport is 21 feet above sea level)
about 25% of Jakarta will vanish by 2050.
Surabaya and Semarang will be almost permanently flooded by 2080.
the capital will have to be moved to Bandung.
2,000 islands will be lost by 2030.
400,000 sq km of land mass lost by 2080, including about 10% of Papua, and 5% of both Java and Sumatra (on the north coast).
Says Nicholas Stern, author of the Stern Report on climate change (2006):

[Response: The only source of sea level figures in that post is the 18 to 59 cm in the IPCC report. But those statements appear to have come from an Indonesian meteorologist Armi Susandi, apparently based on a 50 cm rise. Neither of those figures are alarmist. But whether those headlines are wrong or not depends on where they come from and how they were calculated. I’m not in a position to tell. Find a real citation and we can talk. – gavin]

Abstract
Nine long and nearly continuous sea level records were chosen from around the world to explore rates of change in sea level for 1904–2003. These records were found to capture the variability found in a larger number of stations over the last half century studied previously. Extending the sea level record back over the entire century suggests that the high variability in the rates of sea level change observed over the past 20 years were not particularly unusual. The rate of sea level change was found to be larger in the early part of last century (2.03 ± 0.35 mm/yr 1904–1953), in comparison with the latter part (1.45 ± 0.34 mm/yr 1954–2003). The highest decadal rate of rise occurred in the decade centred on 1980 (5.31 mm/yr) with the lowest rate of rise occurring in the decade centred on 1964 (−1.49 mm/yr). Over the entire century the mean rate of change was 1.74 ± 0.16 mm/yr.

BTW, half the CAPTCHA text is unreadable most of the time. And the sound is garbled.

[Response: Current rates are about 3.2 mm/yr, long term rates over the last century or so are more like 1 to 2 mm/yr. This implies an acceleration- whether or not it is sustained remains to be seen. – gavin]

Gavin (156), your point on Hansen’s comments make a good logical point; but it’s not perfect. An ad hoc “official” climate statesman, and probably the poster boy for climatology testimony has zero business going around musing and speculating.

[Response: I completely disagree. People need to speculate and muse and have their ideas be tested no matter who they are. These kinds of discussion both provoke interest and focus attention on uncertainties that are not being addressed. Non-linear responses of ice sheets to models is a topic that clearly needs more attention and research. – gavin]

“A fair percentage of the comments here are stating we can expect sea levels to rise by a minimum of 2 metres by 2100.”
I don’t know which comments you refer to, but 2 meters by 2100 is generally seen as a high estimate, not a minimum.

“This seems to be based on the idea of a vastly increased global ice melt. Nearly all of the examples of melt seem to involve the NH only, why?”
Because the NH warms faster and the Greenland ice sheet is a lot closer to the equator than antartica.

“Indeed Antarctica, which contains most of the worlds ice, has been geting colder for some time now with evidence of increasing ice levels.”
Could you please provide us with a data source where the increase in ice levels is shown?

It refers to another quite unremarkable comment attributed to Stern (“Island states are very vulnerable to sea level rise and very vulnerable to storms. Indonesia is particularly vulnerable.”) in the site to which you linked.

Roger’s inability to answer the spin problem (#156) is revealing. Clearly there is nothing more to be gained by going on and on about it, but choosing to deflect one failed debate onto another – James Hansen – is indicative that we have moved beyond the realms of science, and onto another agenda entirely (whatever that may be). And coming from a senior climatologist, that is science’s loss.

Speaking of James Hansen, clearly James’ views represent the upper band of what is likely among climate scientists. However, given current the universally unpredicted real-world pace of sea ice decline, his words seem less those of an alarmist for focusing at the upper end, but of a realist. It also seems to me that although this current paper has helped move the debate on, it cannot represent a complete understanding about what could be at stake, given the speed of previous geological events (but happily willing to be shown the error of my ways on that). Further, even this could be a moot point – if, as Hansen (and others) suggest that soon we will pass the point at which we have any ability to slow the rate of change, ethically it doesn’t matter if catastrophic change takes place in 20 years or 2,000 years – it is past generations and especially this one that have lit the inextinguishable fuse, and therefore bear full responsibility.

Which leads to one particularly awkward and inescapable conclusion. Why does James Hansen appear to be alone in his current sense of political urgency? Of course the IPCC has made a very powerful consensus statement, but if Hansen is correct that a target of 2 degrees warming represents climactic suicide, and we have mere months to persuade world governments of drastic action, why is he appearing to be receiving so little practical support from his colleagues? Waiting until the next IPCC report will be too late. Perhaps it is time for a new consensus statement from the world’s leading climate scientists, aimed specifically at urgent political action (a la Hansen) based entirely on science? Are you all really doing *everything* that you can? Would be grateful for the thoughts of Gavin or Stefan on this….

Thanks for your posts David, they are very informative. Are you working in climate change or just an interested observer like me?

Does this 3 C relate to local (Antarctic temperature or estimated global temp?

If the peak of the Eemian was 3 C above today, then in my mind it is probably the most useful guide to what we can expect in terms of sea level rise. The 20 foot rise constrains what we can expect of a 3 C rise to under 6 metres. Presumably during the Eemian peak there was time for “fast response” processes to reach equilibrium (ocean temperature, ice etc.), although not perhaps some slow responses. The Eemian was a similar world to todays. The same ice sheets. Similar geography and sea level. One key difference was the CO2 level.

More detaled kinetics of sea level and temperature at this time would be informative. How accurately are sea levels known and how well can they be aligned with temperatures?

Sea level rise is just one of the negative Forcings on human activity. We have three big ones currently running.

The longest-term is sea level rise – If everything else was not running against us then coping with sea rise would entail the highest level of survival-focussed human activity ever seen – the relocation and reconstruction of about half of all humanity and its essential infrastructure. Let’s say that forcing is 50% upon us in 500 years.

The mid-term threat is climate change on agriculture and infrastructure (Haiti after Gustav and Ike are extreme instance; Spain, Australia’s Murray Darling Basin and the USA South are other examples). Say these effects (drought, flood, storm, fire and the odd case of pestilence and brimstone) will be hitting us at 50%strength in maybe 50-60 years.

The immediate threat is peak energy. 50% into that within 20 years – probably 10, maybe less.

Now each of these forcings will roll us in different ways, and with different intensities and with regionally-specific impacts and senses. It’s a very hard sum to do.

But the trick for us is the sweet way these are sequenced. To cope with climate change we need the energy we won’t have. To let us cope with sea level rise we need the energy and the kindly climate we won’t have.

So if we want to arrive anywhere sensible in the long term, then we need to go for broke starting yesterday. (Lovelock identified the cusp as being around 1965). We need to grab what ever resources and hence what ever source of energy we need right now (coal – who cares) to build the sea-level-rise-life-boat within the time we have. That life boat will include critical food supplies in climate-proof shelters to let us at least survive climate change high and dry.

But if we don’t act now we will use our energy on trips to the movies, and we won’t have any way to produce essentials in the face of climate change, and without that we won’t usefully manage (indeed most won’t survive) the retreat from the coast.

So how do we get that message across? If we don’t our future generations will be in deep trouble. Humans don’t recognise distant threats too well, so maybe we need to focus on addressing the nearer-term threats first. That’s the way they are being presented to us, and that is the ‘correct’ sequence in which to address these threats. Let’s all go out and scream about energy supply-demand divergence and yell about climate change impacts on where we each live. Local action. If we get that right then we will stand a chance when the dykes are over-topped.

Gavin, you are missing the point. The point is this dire prediction from Bali was all over the news, I remember see it many times when they reported on the conference. The point is NO ONE from the AGW community went public to denounce those numbers are wild speculation. Hence the public at large gets the impression that you people agree with thse dire predictions. Thus you are all complacent with these unscientific dire alarmist predictions.

[Response: Not at all. I have never seen those claims before, and if someone had brought them up here I would have questioned them (but actually since you still haven’t shown me the source, I have no idea whether they are valid or not – there are an awful lot of islands in Indonesia). There are scores of examples where we have countered exaggerations (sea level, climate sensitivity etc) and you only need to spend a small amount of time here to see that. Your claim that “NO ONE” does this is specious. I am neither complacent, nor complicit, with ‘alarmist’ predictions. – gavin]

Try this: put one ice cube in an empty glass, another in a glass full of water. You’ll see the second melt completely long before the first. As an amateur I don’t know about the fine points here, but essentially, other things being equal, the water is a much more efficient “heat donor.” Of course, you can change the ability of the air, too–by using a fan to blow a *stream* of air across the first ice cube, for instance.

Another point is that glaciers don’t stay “where they are” anyway–they are dynamic systems, so all those interacting factors–glacial flow, precipitation scenarios, radiative forcings, atmospheric conditions–would need to be considered to make predictions.

Gavin has let the cat out of the bag. His link to the long term trend in sea level shows no acceleration, but a constant rate of increase. Published papers show there is a decadal fluctuation in the rate of sea level rise, and the current rate has not broken through that variation. Thus the current rate cannot be attributed to AGW. Plus, there is a serious logical problem with linking this rate to anthropic global warming. CO2 emissions over the same period has not been linear, but in fact follows a classic growth curve.

From 1850 to 1945, when we experienced a large proportion of the warming, our emission level went to 1200 MMTC/Yr, a mere 14% of today’s level. From 1945 onward we saw an 8 TIMES increase in CO2 emissions which comprises 86% of the total increase since 1850. Yet half that time, 1945 to 1975, the planet cooled right when the rate of CO2 emissions increased 4 TIMES. Half of the increase in CO2 has been in the last 40 years, the last 10 of which the planet has not warmed in spite of a 20% increase in CO2 emissions.

Since sea level rise has not changed its’ rate over this entire period one has to question if any of the current rate has anything to do with AGW. If there were a correlation one would have expected to see some sort of “hockey stick” in the rate of sea level rise. But it’s not there.

This has serious consequences for AGW theory

[Response: Again, no. Sea level rise so far is associated with the very slow (but persistent) take up of heat by the oceans (which if you hadn’t noticed is a big place). The amount of SLR in recent decades fits very nicely with the expectations of models, measurements of ocean temperature change and estimates of ice sheet melt. The increase in the future due to thermal expansion will see a relatively slow growth, but the changes from the ice sheets is increasing much faster. Your imagined ‘expectation’ coincides with no ‘expectation’ that I have ever seen. Read the IPCC report (section 10.6) to inform yourself about what people actually expect. – gavin]

Gavin, how come no one at Bali came out and corrected these wild predictions at that time then? That’s the problem. It got into the MSM and was disseminated around the world. I waited to hear any rebuttal to these from anyone, and nothing appeared in the MSM. Thus the public thinks this is the consensus! Major damage is being done to science because of these wild unscientific alarmist predictions. What you and Hansen need to do to correct this is hold a news conference with the MSM and make it clear to the PUBLIC, not your readers of RC, what the actual scientific position is. You have a problem with doing that?

I posted the links of the source.

[Response: I have no idea what people did at Bali. I wasn’t there. Your source is a third hand blog post and its insinuation that these numbers came from Stern is simply wrong. Something so specific must have come from a regional, likely Indonesian, assessment and you insist that they are wrong but with no source or cite to show that to be the case. If those claims are based on the sea level rises quoted in your ‘source’ then they aren’t wrong. I give public talks all the time and have a book coming out on the same topic. I hardly think you can accuse me of being shy. – gavin]

re #167–
Alan, I’ve put some of your words in quotes & responded point by point.

“I would hope that this lack of discussion in SH ice, which after all is the overwhelming factoe in any sea level rise based on ice melt, is not due to the fact there is no evidence of decreasing ice levels in the SH. Indeed Antarctica, which contains most of the worlds ice, has been geting colder for some time now with evidence of increasing ice levels.”

*National Snow and Ice Data Center shows a decreasing trend for ice *globally.* Moreover, the picture in Antarctica is quite mixed–the peninsula has been warming quite rapidly and has exhibited some very dramatic ice loss.

“The other current indicators do not seem to support any such speculations. Sea temperatures have shown a slight cooling over the last few years. Global temperatures have stalled since 2001 with a slight cooling in fact.”

*You hear this from denialist sources a lot. But trends are not calculated by point-to-point comparisons; you have to consider the shape of the plotted data curve as a whole, and for a sufficiently long period of time. (That said, I don’t understand why you pick 2001, given that 2005 was the warmest on record in some datasets–if you are going to cherry-pick, go for 2005 at least!) The computed global merged land-sea trend is, if I remember correctly, currently at .17 degrees warming per decade.

“Basing everything on computer models which are slowly moving away from actual Earth conditions does not seem to be ‘proper’ science to me.”

*Explore this site to learn about the other lines of physical evidence–it is far from just model-based. It is interesting, and, to me at least, quite eye-opening.

“I actually don’t seem to see much effort being put into trying to explain and calculate the reasons and factors which seem to have stopped the, hypothesised, inexorable rise in global temperatures caused by Mankinds CO2 emissions. Emissions which have continued to increase post the models.”

*That’s because your premise–the “seem to have stopped” part–is just wrong. See above, or check out the 2007 climate report at the National Climate Data Center site.

“. . .the whole AGW theory. . . is based on the theory that CO2 was the ‘last man standing’ when all other natural factors were eliminated because of their calculated maximum effect.”

*Again, explore this site to find out why this statement is not really correct. AGW theory is fundamentally based upon firmly-validated physics that show CO2 (and other GHGs as well) do in fact have characteristics enabling them to “force” the climate. The checking of other explanatory factors which you reference is the obvious (and scientifically responsible) next step–and it has been carried out to the general satisfaction of the climate science community–even skeptics like Professors Spencer and Lindzen agree with the theory to this point. (They are essentially postulating that water vapor feedbacks occurring through some as-yet undiscovered mechanism will somehow save our collective butt. Their position, paraphrased, is “AGW is real, & is happening, but won’t be so bad.”)

“I suppose the idea out there is that, if a combination of natural factors could produce that amount of cooling then, it is just as likely that a similar combination of factors could cause a similar amount of warming. Something that the hypothesis of AGW can not allow.”

*If you are saying that AGW theory presumes that natural variability is unimportant, then you are wrong. Natural variability–AKA “noise,” as contrasted with a climate “signal”–continues and nobody disputes this. Natural variability is in fact exactly what make trends hard to spot, and crucial to measure correctly. When you claim a “cooling trend” based on point-to-point comparison, I am afraid it is you who is failing to take adequate account of this natural variability.

Hope this helps. Please do read the explanations found elsewhere on this site. Spencer Weart’s “Discovery of Global Warming” is also an excellent account, and deals very clearly with many of these points; you can access it from this site, and Dr. Weart has in fact just done a very nice RealClimate guest commentary on the inherent complexity of numerical prediction in climate study.

Gavin, so you are agreeing then that from 1850-1945 the amount of CO2 could not affect the rate of sea level. Since that rate has not changed except decadal variation since 1850 then the current rate of sea level cannot be from AGW? It’s a logical consequence.

“At best, the determination and attribution of global mean sea level change lies at the very edge of knowledge and technology. The most urgent job would appear to be the accurate determination of the smallest temperature and salinity changes that can be determined with statistical significance, given the realities of both the observation base and modeling approximations. Both systematic and random errors are of concern, the former particularly, because of the changes in technology and sampling methods over the many decades, the latter from the very great spatial and temporal variability implied by Figs. 2, 6, 8. It remains possible that the data base is insufficient to compute mean sea level trends with the accuracy necessary to discuss the impact of global warming–as disappointing as this conclusion may be.”

This begs an important question for you. How many more years of no acceleration will it take to abandon AGW theory?

[Response: But I said nothing of the sort. CO2 (and other GHGs) increases up to 1945 are a significant forcing but not substantially larger than other forcings on a decadal time scale (solar, volcanic etc.). The GHG signal only starts to be dominant by around 1980, but that isn’t the same as saying it had no effect before. However, your assessment of the solidity of the decadal SLR trends prior to the satellite trends is more confident than is warranted. Attribution of the latest 30 years or so is possible – before that we don’t have enough data on ocean temperatures or ice sheets to do it. (PS. AGW is based on the radiative impact of CO2 and other atmospheric constituents – none of those things depend on sea level rise. PPS. Look up what ‘beg the question’ means.) – gavin]

Or are already breaking down. Again I ask, how many years will it take to melt all the ice and produce Hansen’s prediction? There must be some sort of physical limit. Show us why my 1000 year prediction is incorrect. It is imperative in science to be clear. Hansen el al making such large claims with out some sort of time reference is irresponsible and highly unscientific.

[Response: No. Collapsing ice sheets have lead to SLR of meters per century in the past (MWP 1A, or even the early Holocene final collapse of the Laurentide). We know that 4-6 meters of sea level are consistent with a further warming of the poles of 3 to 5 deg C (compare to the Eemian). Collapse of the WAIS is not a fiction. It has happened before. But though no-one can say how fast it happened, does not mean that it is highly irresponsible to discuss it. That discussion is motivating a great deal of work (including Pfeffer et al, but also Rignot, Payne, and many others) to be more quantitative. The science is not yet done, and yet you are convinced that it can’t happen. Based on what? – gavin]

Gavin (176), you have a valid point (again). Whether musing and speculating is helpful or not entirely depends on the audience; and, I agree, with the correct audience, it’s not only O.K., it’s highly desirable.

Richard Wakefield enquires: “This begs an important question for you. How many more years of no acceleration will it take to abandon AGW theory?”

Sigh. Yet another denialist who thinks philosophy of science began and ended with Popper. Richard, how about if we just say that we will embrace a new theory just as soon as somebody comes up with it and it turns out to explain the data–all of it, produced by over 150 years of climate–better than the current one. That’s how science works. It is extremely unlikely that said theory will look a whole lot different than the current one, but you or anyone else is free to try and develop one. Go ahead. We’ll wait.

The 3 K was what was measured in the Vostok ice core. The northern Greenland NGIUSP ice core gives 5 K increase over present in the Eemian. The IPCC AR4 shows a modeling of the Greenland ice sheeet during the Eemian, much reduced.

Due to isostatic rebound it is currently not possible to state what the sea highstand was with precision; 4–6 meters depending upon just where one looks; I know nothing about the ‘alignment of temperature’, but opine that it would lag somewhat.

Due the peak of the Eemian in Antarctica, the CO2 concentration was 287.1 ppm according to Petit et al. Dr. James Hansen has suggested that at today’s elevated CO2 concentration that Antactic ice sheets are at serious risk; you can obtain copies of his papers on his web site.

“The GHG signal only starts to be dominant by around 1980, but that isn’t the same as saying it had no effect before.” Provide peer reviewed evidence it did prior to 1980 and by how much.

[Response: Tyndall (1863). – gavin]

“However, your assessment of the solidity of the decadal SLR trends prior to the satellite trends is more confident than is warranted. ” Then publish a paper refuting Holgate, until you do you are only speculating which hence can be rejected.

“Attribution of the latest 30 years or so is possible – before that we don’t have enough data on ocean temperatures or ice sheets to do it.” So your are claiming that in situ measurements from the last 110 years, such as

are wrong? Only satellite data can be trusted to be correct? LOL!! That’s funny. There is no acceleration in any in situ measuerments. Satelite measuruments are way too short and not reliable. That’s what’s in the peer reviewed papers!

” It is difficult to detect the geographic “fingerprint” of long-term climate change signals using altimeter data from a single satellite mission such as T/P, because the mission length will probably be insufficient to easily differentiate these signals from interannual and decadal variations.”

“Figure 2 shows variations in global mean sea level observed over the first 8 years of the T/P mission [Nerem et al., 1999]. The 15-20 mm rise, and subsequent fall, of mean sea level during the 1997-1998 ENSO event was interesting in itself, but also somewhat dissappointing since it will require us to have a much longer time series of altimeter measurements in order to average through the ENSO events and detect the true long term change.”

Fact is, if the rate of sea level does not change AGW is in deep trouble. Melting ice is everything to the theory.

[edit – keep it calm]

Re 192:

“We know that 4-6 meters of sea level are consistent with a further warming of the poles of 3 to 5 deg C” That’s an assumption and no evidence to support that this will actually happen. It’s a prediction from models only.

[Response: No. It’s what you get from looking at the Eemian. No models necessary. – gavin]

“Collapse of the WAIS is not a fiction. It has happened before. But though no-one can say how fast it happened, does not mean that it is highly irresponsible to discuss it. ” It most definitely is if you do not give a time frame and leave in the public mind that it will be sooner than you know or suspect. That’s tantamount to deliberate misrepresentation. So give us a time frame! If you cannot even give some ball park realistic time frame then you should not be saying anything, period!

You do realize that by allowing continued misrepresentation you will be subject to two things.

1) once the real evidence comes forth, you will look like fools. That I really do not care about. But what I do care about is…

2) once the real evidence comes out and you are shown to be wrong you will have done irreparable harm to science for a long long time. Other scientists will be rejected for funding in the future because people like you who refuse to come clean will have damaged science so much in the eyes of the public. You know that is true.

Give your predictions [edit] and give time frames. If you do not know say so, and encourage all your AGW supporters to do the same thing. You guys like to throw at us skeptics “what if you are wrong”. I throw it right back at you.

[Response: Conscientious science requires that address all possibilities, and yes, you need to give a sense of how likely these things are. There is clearly a possibility of significant ice sheet collapse (the Eemian shows that), but we don’t understand how fast these things can happen. You would have us not mention it because we can’t say everything about it? This is stupid. How is science supposed to procede if no-one discusses what the unknowns are or where the uncertainties lie? In five years time we’ll have a better idea, but right now we can’t give you a time scale. Deal with it. I’m not going to make something up to make you happy. – gavin]